The invention relates generally to network communications. More specifically, the invention relates to a system and method for predictive end-to-end network management for optical networks employing monitoring, correlating and alarming performance parameters.
A Synchronous Optical Networking (SONET) system includes switches, multiplexers and repeaters, all connected by optical fiber. SONET topologies are typically configured as self-healing, dual-ring networks using dual fiber optic cables.
The SONET physical layer is divided into four sublayers. The lowest sublayer is the photonic sublayer. The three remaining sublayers correspond to the sections, lines and paths. An optical fiber going directly from any device to any other device is referred to as a section. A run between two multiplexers is referred to as a line and the connection between a source node and a destination node with one or more multiplexers and repeaters is referred to as a path. The section sublayer handles a single point-to-point fiber run, generating a standard frame at one end and processing it at the other. Sections can start and end at repeaters, which amplify and regenerate the bits, but do not change or process them. The line sublayer is concerned with multiplexing multiple tributaries onto a single line and demultiplexing them at the other end. To the line sublayer, the repeaters are transparent. When a multiplexer outputs bits on a fiber, it expects them to arrive at the next multiplexer unchanged, no matter how many repeaters are used in between. The protocol in the line sublayer is between two multiplexers and deals with issues such as how many inputs are being multiplexed together and how. The path sublayer and protocol deal with end-to-end issues.
SONET and Synchronous Digital Hierarchy (SDH) have a limited number of defined architectures. These architectures allow for efficient bandwidth usage as well as the ability to transmit traffic even when part of the network has failed.
A major advantage of SONET networks is their standardized Automatic Protection Switching (APS) schemes. SONET systems can be configured as point-to-point terminals, linear add-drop chains and rings. Two types of self healing ring topologies are Unidirectional Path Switched Ring (UPSR) and Bi-directional Line Switched Ring (BLSR).
FIG. 1 shows a four node ring. Each node on the ring is connected to its respective adjacent nodes by two optical fibers, one transmits and one receives. The outer fiber loop may be referred to as ring 1 and the inner fiber loop is referred to as ring 2. In this example a path (circuit) is to be set up between nodes A and C. The input at node A travels clockwise on ring 1 and egresses at node C. The input to node C also travels clockwise on ring 1. The signal egresses at node A completing the path, establishing communications between source node A and destination node C. All that is required for the path to be operational is the ring 1 fiber unidirectional path.
Ring 1 is the working path and ring 2 is the protection path. Protection is facilitated by adding a bridging circuit at the SONET Network Element (NE) source node. Protection traffic travels anticlockwise on ring 2. A selector switch is implemented at the SONET NE destination node which chooses the signal that exits. Selection is made upon SONET Performance Monitoring (PM) path parameters such as Alarm Indication Signal (AIS), Loss of Pointer (LOP), Loss of Signal (LOS), Signal Degrade (SD), and others.
FIG. 2 shows a fiber break between nodes B and C. When the break occurs, the receiver at node C ring 1 detects an Optical Carrier (OC) OC-N LOS and inserts an Alarm Indication Signal-Path (AIS-P) onto all affected paths. When a drop node (in this case node C) detects the AIS-P on the working path, the selector performs a path switch to ring 2. Because node C is adjacent to the fiber break, all of its selectors will make a path switch. The output of node C on ring 1 has an AIS-P on all of its path signals except for those added at node C.
Node A will not detect the fiber break LOS, but the receiver on ring 1 will detect the AIS-P that is inserted onto the path at node C. Node A will receive its signal from B on ring 2. Node A is not adjacent to the fiber break so all its path selectors will switch based upon path integrity of each individual path independent of the status of any other path. Each node in a SONET ring makes the decision to switch independently without communicating to any of the other nodes.
Due to the large volume of PM parameter data possibly accumulated for an OC-N line, for example, a SONET OC-48 path from New York, New York to Los Angeles, Calif., having many lines, it is difficult to analyze all of the accumulated PM parameter data. Even in the absence of serious fiber breaks, the amount of PM parameter data is voluminous. For slight path deficiencies, statistical counters and metrics have not been managed. What is desired is a system and method that provides a customer with predictive end-to-end path management of his SONET networks.